This invention relates generally to semiconductor laser structures and more particularly to laser structures having buried back biased current confinement means formed in situ that function as optical and current confinement mechanisms for such laser structures.
The employment of buried current blocking layers or current confinement regions to channel current through a selected active region of semiconductor laser devices, such as heterostructure quantum well lasers and array lasers, are well known in the art. However, there is no report or disclosure known by us that attempts or contemplates the fabrication of such current confinement means in situ during growth without at least the requirement of an additional step of, for example, photolithography or chemical etching or masking, to provide such current confinement structures. What is desired is a process, particularly as implemented in MBE or MOCVD, wherein layer patterning can be achieved in situ without growth interruption by some off-line or nongrowth procedure or process.
There are two examples known to us where patterning may be achieved by quasi-in situ thermal processing wherein thermal etching is employed to selectively remove GaAs. In one example, a n-GaAs layer over a p-AlGaAs layer is first, selectively chemically etched in a particular region followed by thermal etching to remove the remaining thin GaAs left from chemical etching before proceeding with regrowth of the p-AlGaAs layer. This forms a buried reverse biased current confinement mechanism in a double heterostructure laser. H. Tanaka et al, "Single-Longitudinal-Mode Self Aligned AlGa(As) Double-Heterostructure Lasers Fabricated by Molecular Beam Epitaxy", Japanese Journal of Applied Physics, Vol. 24, pp. L89-L90, 1985. In the other example, a GaAs/AlGaAs heterostructure partially masked by a metallic film is thermally etched in an anisotropic manner illustrating submicron capabilities for device fabrication. A. C. Warren et al, "Masked, Anisotropic Thermal Etching and Regrowth for In Situ Patterning of Compound Semiconductors", Applied Physics Letters, Vol. 51(22), pp. 1818-1820, November 30, 1987. In both of these examples, AlGaAs masking layers are recognized as an etch stop to provide for the desired geometric configuration in thermally etched GaAs, although it is also known that, given the proper desorption parameters, AlGaAs may also be thermally etched at higher temperatures with different attending ambient conditions visa vis GaAs.
However, none of these techniques employ in situ photo induced evaporation as a technique in a film deposition system to incrementally reduce, on a minute scale, film thickness in patterned or selective locations at the growth surface either during or after film growth, producing smooth sculptured surface morphology which is a principal objective of this invention.
It is another object of this invention to bring about in situ removal or desorption of selected surface regions or layers of compound semiconductors employing induced evaporation enhancement in metalorganic chemical vapor deposition (MOCVD) epitaxy and to apply this method in the fabrication of optical waveguides and buried heterojunction lasers and laser arrays with in situ fabricated buried back biased junctions for internal current confinement.